This invention relates to a method for making a magnesium di[tetrakis(Faryl)borate], which can be further reacted with an organic cation salt to produce the corresponding organic cation tetrakis(Faryl)borate. When the organic cation is a protic ammonium cation or a triarylmethyl cation, the tetrakis(Faryl)borate salt is useful as a cocatalyst for metallocene-catalyzed polymerization. When the organic cation is an onium cation, the tetrakis(Faryl)borate salt is useful as an initiator in the crosslinking of polyorganosiloxanes.
It is known that when a halomagnesium salt of a tetrakis(aryl)borate anion is obtained, other magnesium salts are usually also present. Often, the removal of these other magnesium salts is necessary because they interfere with the intended use of the halomagnesium salt of the tetrakis(aryl)borate anion. Reaction of the halomagnesium tetrakis(aryl)borate with an alkali metal salt to form an alkali metal tetrakis(aryl)borate is a separation method that has been used. For various descriptions of this method, see Nishida et al., Bull. Chem. Soc. Jpn., 1984, 57, 2600; Goldberg et al., Zhurnal Organicheskoi Khimii, 1989, 25, 1099; Fujiki et al., J. Fluorine Chemistry, 1992, 57, 307; and EP 913,400. A method which cleanly separates other magnesium salts from the halomagnesium salt of the tetrakis(aryl)borate without the introduction of a reagent such an alkali metal salt would be desirable.
Once a suitably pure tetrakis(aryl)borate salt is obtained, it can be reacted with an appropriate compound to yield an organic cation salt of the tetrakis(aryl)borate. It is often desirable to purify these organic cation tetrakis(aryl)borates. It is known that phenyl(dimethyl)ammonium tetrakis(pentafluorophenyl)borate can be purified via the formation of a liquid clathrate. The liquid clathrate is formed in toluene at temperatures typically above 55xc2x0 C.; at temperatures less than about 55xc2x0 C., the compound precipitates. While the liquid clathrate provides relatively pure phenyl(dimethyl)ammonium-tetrakis(pentafluorophenyl)borate, it is inconvenient to keep the clathrate-containing solution and apparatus at elevated temperatures while performing necessary manipulations. A more convenient purification method is desirable.
This invention provides for the formation of a magnesium di[tetrakis(Faryl)borate], which can be, but need not be, isolated. The magnesium di[tetrakis(Faryl)borate] can be reacted, in isolated or unisolated form, with a salt of a desired cation to form the desired cation tetrakis(Faryl)borate. Certain of these tetrakis(Faryl)borates can be conveniently purified via the formation of a liquid clathrate at ambient temperatures.
A first embodiment of this invention is a process which comprises contacting i) a solution comprising a liquid organic medium, which is substantially immiscible with water, and a halomagnesium tetrakis(Faryl)borate, and ii) water, in such proportions that a two-phase mixture is obtained. A solution of a magnesium di[tetrakis(Faryl)borate] in the organic phase of a two-phase water/liquid organic medium is produced. Each aryl group of the tetrakis(Faryl)borate has bonded directly to an aromatic ring at least two fluorine atoms, or at least two perfluorohydrocarbyl groups, or at least one fluorine atom and at least one perfluorohydrocarbyl group. The liquid organic medium is comprised of one or more liquid dihydrocarbyl ethers, one or more liquid hydrocarbons, one or more liquid halogenated hydrocarbons, or mixtures thereof.
The borate anion has four fluorine-containing aryl groups, each of which has bonded directly to an aromatic ring at least two fluorine atoms, or at least two perfluorohydrocarbyl groups, or at least one fluorine atom and at least one perfluorohydrocarbyl group. It is preferred that at least two fluorine atoms, or at least two perfluorohydrocarbyl groups are bonded directly to an aromatic ring. Each position on the aromatic ring(s) of the Faryl group that is not a fluorine atom or a perfluorohydrocarbyl group is substituted by a hydrogen atom, a hydrocarbyl group, an alkoxy group, or a silyl group. The Faryl groups may be the same or different from each other; it is preferred that all four Faryl groups are the same.
Another embodiment of this invention is a process which comprises mixing at least a portion of the magnesium di[tetrakis(Faryl)borate] produced in the first embodiment in a liquid medium with a salt selected from a) a protic ammonium salt, b) an onium salt, and c) a triarylmethyl salt, wherein the triarylmethyl cation has three aryl groups bound to a central carbon atom, to produce a protic ammonium tetrakis(Faryl)borate, an onium tetrakis(Faryl)borate, or a triarylmethyl tetrakis(Faryl)borate. The protic ammonium cation has the formula [R3NH]⊕, in which each R is independently a hydrocarbyl group containing up to about thirty carbon atoms, and the onium cation has the formula [ERn]⊕, wherein E is an element of any of Groups 15-17 of the Periodic Table, wherein each R is independently a hydrocarbyl group containing up to about thirty carbon atoms, and wherein n is equal to the valence of E plus one. For labeling of the groups of the Periodic Table, see for example, the Periodic Table appearing in Chemical and Engineering News, 1985, 69, 26.
Still another embodiment of this invention is a process which comprises mixing, in a liquid medium, at least a portion of the magnesium di[tetrakis(Faryl)borate] produced in the first embodiment and at least one metal salt. An inorganic metal tetrakis(Faryl)borate is produced.
Yet another embodiment of this invention is a process which comprises mixing, in a liquid medium, at least a portion of the metal tetrakis(Faryl)borate produced in the preceding embodiment with a salt selected from a) a protic ammonium salt, b) an onium salt, and c) a triarylmethyl salt, to produce a protic ammonium tetrakis(Faryl)borate, an onium tetrakis(Faryl)borate, or a triarylmethyl tetrakis(Faryl)borate. The protic ammonium cations, onium cations, and triarylmethyl cations are as described above.
Further embodiments of this invention will be apparent from the ensuing description and appended claims.
The liquid organic medium of the solution that also comprises a halomagnesium tetrakis(Faryl)borate is comprised of one or more liquid dihydrocarbyl ethers, one or more liquid hydrocarbons, one or more halogenated hydrocarbons, or mixtures thereof. Those ethers, hydrocarbons, and halogenated hydrocarbons that are substantially immiscible with water, such that a two-phase mixture will be formed, are preferred. Ethers that may be used include, for example, diethyl ether, di-n-propyl ether, diisopropyl ether, tert-butyl ethyl ether, diheptyl ether, and similar compounds. Preferred ethers are diethyl ether and diisopropyl ether, especially diethyl ether. Suitable hydrocarbons include pentane, hexane, methylcyclohexane, heptane, octane, cyclooctane, nonane, benzene, toluene, and xylenes. Halogenated hydrocarbons that may be used include dichloromethane, trichloromethane, 1,2-dichloroethane, 1-bromo-2-chloroethane, 1-bromopropane, (chloromethyl)cyclopropane, 1-bromobutane, 1-bromo-2-ethylbutane, 1,1-dichloro-3,3-dimethylbutane, cyclobutyl chloride, neopentyl chloride, 1-bromo-5-chloropentane, cyclopentyl bromide, 1,6-dibromohexane, trans-1,2-dichlorocyclohexane, 1-chloroheptane, and 1,8-dichlorooctane.
The proportions of water and liquid organic medium are such that either component can be present in a larger amount than the other; however, a large excess of either is unnecessary. Preferred ratios of water to liquid organic medium are in the range of from about 0.2 parts to about three parts by volume of water per part by volume of liquid organic medium.
The halogen atom of the halomagnesium moiety of the halomagnesium tetrakis(Faryl)borate may be a chlorine atom, bromine atom, or iodine atom. Preferred halogen atoms are chlorine and bromine; most preferred is a bromine atom. Thus, the most preferred halomagnesium moiety is a bromomagnesium moiety.
Throughout this document, the term xe2x80x9cFaryl groupxe2x80x9d shall be understood to mean, as described above, a fluorine-containing aryl group, which has bonded directly to an aromatic ring at least two fluorine atoms, or at least two perfluorohydrocarbyl groups, or at least one fluorine atom and at least one perfluorohydrocarbyl group. It is preferred that at least two fluorine atoms or at least two perfluorohydrocarbyl groups are bonded directly to an aromatic ring. Each position on the aromatic ring(s) of the Faryl group that is not a fluorine atom or a perfluorohydrocarbyl group is substituted by a hydrogen atom, a hydrocarbyl group, an alkoxy group, or a silyl group. The aromatic ring of the Faryl group may be, but is not limited to, benzene, naphthalene, anthracene, biphenyl, phenanthrene, or indene. Benzene is the preferred aromatic moiety. The perfluorohydrocarbyl groups include alkyl and aryl perfluorocarbons; suitable perfluorohydrocarbyl groups are, for example, trifluoromethyl, pentafluoroethyl, pentafluorophenyl, and heptafluoronaphthyl. The hydrocarbyl groups of the aryl groups are preferably C1 to C18 alkyl groups or C6 to C20 aryl or aralkyl groups. Examples of suitable hydrocarbyl groups are methyl, ethyl, isopropyl, tert-butyl, cyclopentyl, methylcyclohexyl, decyl, phenyl, tolyl, xylyl, benzyl, naphthyl, and tetrahydronaphthyl. The alkoxy groups preferably have C1 to C6 alkyl moieties. Some examples of alkoxy groups are methoxy, ethoxy, isopropoxy, methylcyclopentoxy, and cyclohexoxy. The silyl groups preferably have C1 to C18 alkyl groups or C6 to C20 aryl or aralkyl groups. Suitable silyl groups include trimethylsilyl, triisopropylsilyl, tert-butyl(dimethyl)silyl, tridecylsilyl, and triphenylsilyl. Examples of Faryl groups that may be present on the borate moiety in this invention include 3,5-bis(trifluoromethyl)phenyl, 2,4,6-tris(trifluoromethyl)-phenyl, 4-[tri(isopropyl)silyl]-tetrafluorophenyl, 4-[dimethyl(tert-butyl)silyl]-tetrafluorophenyl, 4xe2x80x2-(methoxy)-octafluorobiphenylyl, 2,3-bis(pentafluoro-ethyl)naphthyl, 2-(isopropoxy)-hexafluoronaphthyl, 9,10-bis(heptafluoropropyl)-hepta-fluoroanthryl, 9,10-bis(p-tolyl)-heptafluorophenanthryl, and 1-(trifluoromethyl)-tetrafluoroindenyl. It is preferred that at most two substituents on the ring of the aryl group are hydrocarbyl, perfluorohydrocarbyl, or alkoxy, while the rest of the substituents are fluorine atoms.
It is highly preferred to have Faryl groups in which the all of the substituents are fluorine atoms. Examples of such groups are pentafluorophenyl, 4-nonafluorobiphenylyl, 2-nonafluorobiphenylyl, 1-heptafluoronaphthyl, 2-heptafluoronaphthyl, 7-nonafluoroanthryl, 9-nonafluorophenanthryl, and analogous groups. The most highly preferred perfluoroaryl group is pentafluorophenyl; thus, the most highly preferred borate is tetrakis(pentafluorophenyl)borate.
A magnesium di[tetrakis(Faryl)borate] is produced by contacting water and the solution comprising a liquid organic medium and a halomagnesium tetrakis(Faryl)borate. These components are usually at room temperature when mixed together. In the resultant two-phase mixture, the magnesium di[tetrakis(Faryl)borate] is in the organic phase, which can easily be separated from the aqueous phase. Removal of the liquid organic medium from the separated organic phase yields solid magnesium di[tetrakis(Faryl)borate]. Magnesium salts produced in the formation of the magnesium di[tetrakis(Faryl)borate] migrate to the aqueous layer. When other magnesium salts are present in the liquid organic medium, they are also expected to be in the water layer of the resultant two-phase mixture.
During the course of the reaction, some heat may be produced, raising the temperature of the reaction mixture. The mixture may be heated, provided that the temperature does not exceed the thermal decomposition temperature of the magnesium di[tetrakis(Faryl)borate]. A preferred contact time for the components of the reaction is in the range of from about ten minutes to about eight hours. More preferably, the contact time is from about fifteen minutes to about six hours.
For the contacting of a magnesium di[tetrakis(Faryl)borate] and a triarylmethyl salt, the liquid medium is comprised of one or more liquid hydrocarbons, halogenated hydrocarbons, ethers, or mixtures thereof. Suitable hydrocarbons include linear, branched, and cyclic saturated hydrocarbons, and aromatic hydrocarbons. Examples of suitable hydrocarbons include pentane, hexane, cyclohexane, methylcyclohexane, heptane, cyclooctane, nonane, benzene, toluene, xylene, and the like. Halogenated hydrocarbons that are suitable include dichloromethane, trichloromethane, 1,2-dichloroethane, 1-bromo-2-chloroethane, 1-bromopropane, (chloromethyl)cyclopropane, 1-bromobutane, 1-bromo-2-ethylbutane, 1,1-dichloro-3,3-dimethylbutane, cyclobutyl chloride, neopentyl chloride, 1-bromo-5- chloropentane, cyclopentyl bromide, 1-fluorohexane, 1,6-dibromohexane, trans-1,2- dichlorocyclohexane, 1-chloroheptane, and 1,8-dichlorooctane. Examples of ethers that may be used include diethyl ether, ethyl n-propyl ether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether, tetrahydrofuran, methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, cyclohexylmethyl ether, glyme (the dimethyl ether of ethylene glycol), diglyme (the dimethyl ether of diethylene glycol), triglyme, and tetraglyme. Preferred as the liquid organic solvent are saturated hydrocarbons, particularly those containing up to about ten carbon atoms. Also preferred are liquid aromatic hydrocarbons; particularly preferred is toluene. Preferably, the liquid organic solvent is dry, and it is preferred that the reaction is conducted in an inert atmosphere comprised of one or more inert gases, such as, for example, nitrogen, helium, or argon.
The term xe2x80x9ctriarylmethyl cationxe2x80x9d refers to carbocations which have three aryl groups bound to a central carbon atom. The aryl groups of the triarylmethyl cation have from six to about twenty carbon atoms, can be the same or different, and can be substituted or unsubstituted. Examples of suitable aryl groups include phenyl, tolyl, xylyl, naphthyl, and 2-ethylnaphthyl; preferred are tolyl and phenyl; most preferred is phenyl. The most preferred triarylmethyl cation is a triphenylmethyl cation.
Many inorganic anions can be appropriate counterions for a triarylmethyl cation; examples of suitable inorganic anions include chloride, bromide, iodide, tetrafluoroborate, hexafluorophosphate, and the like. Preferred inorganic anions are the halides, especially chloride; thus, the preferred salt is triphenylmethyl chloride.
The magnesium di[tetrakis(Faryl)borate] can be combined with the triarylmethyl salt and the liquid medium in any order. Mixing of magnesium di[tetrakis(Faryl)borate] with the triarylmethyl salt prior to the addition of the liquid medium may cause the formation of a cake. Thus, it is preferred that both the liquid medium and the triarylmethyl salt are present in the reaction vessel before the magnesium di[tetrakis(Faryl)borate] is added.
Protic ammonium salts of the tetrakis(Faryl)borate can be formed from the magnesium di[tetrakis(Faryl)borate]. These ammonium cations have the general formula [R3NH]⊕, wherein each R is independently a hydrocarbyl group containing up to about thirty carbon atoms. R is preferably an aliphatic or aromatic hydrocarbyl group; preferred hydrocarbyl groups include methyl and phenyl. Examples of suitable protic ammonium cations include, but are not limited to, trimethylammonium, triethylammonium, cyclohexyl(dimethyl)ammonium, tri(n-octyl)ammonium, phenyl(dimethyl)ammonium, diphenyl(ethyl)ammonium, and triphenylammonium cations. As described above for the triarylmethyl salt, many inorganic anions can be appropriate counterions for the protic ammonium cation. Again, the halides, especially chloride, are preferred inorganic anions; thus, the preferred salt is generally a protic ammonium chloride.
The protic ammonium salt can be formed shortly before reacting it with the magnesium di[tetrakis(Faryl)borate]; this is accomplished by reacting R3N, wherein R is defined as for the protic ammonium cations, with a protic acid to form the protic ammonium cation. Preferred protic acids include hydrochloric acid, hydrobromic acid, hydroiodic acid, fluoboric acid, and hexafluorophosphoric acid; hydrochloric acid is a particularly preferred protic acid. Preferably, the protic ammonium cation is formed in aqueous solution.
The liquid medium for contacting the protic ammonium salt and magnesium di[tetrakis(Faryl)borate] can be any of a large variety of solvents, so long as they do not interfere with or decompose the desired reaction products. The exclusion of water is not necessary. When water is at least a part of the liquid mixture, the aqueous portion is preferably provided by the freshly-made protic ammonium salt solution. When ether is at least a part of the liquid medium, it may be provided by the alkali metal tetrakis(Faryl)borate solution. In such a case, though it is not considered practical to do so, the alkali metal tetrakis(Faryl)borate may be isolated from the ethereal phase in which it was made and dissolved in fresh ether.
Other salts, generally referred to as onium salts, can be reacted with the magnesium di[tetrakis(Faryl)borate] to yield the corresponding onium tetrakis(Faryl)borate. Onium cations are defined by the formula [ERn]⊕, wherein E is an element of any of Groups 15-17 of the Periodic Table, each R is independently a hydrocarbyl group containing up to about thirty carbon atoms, and n is equal to the valence of E plus one. R is preferably an aliphatic or aromatic hydrocarbyl group. As an example of n, when E is sulfur, which has a valence of two, n is three. As described previously for both the triarylmethyl salts and the protic ammonium salts, many inorganic anions may be appropriate counterions for the onium cation. Preferred inorganic anions are the halides, especially chloride; thus, the preferred salt is generally an onium chloride. To form the onium tetrakis(Faryl)borates, standard cation exchange methods can be used. Choice(s) of solvent and temperature will vary with the particular system of onium salt and tetrakis(Faryl)borate chosen. Examples of suitable onium salts include, but are not limited to, diphenyliodonium chloride, tris(p-tolyl)sulfonium bromide, and tetraethylphosphonium chloride.
Generally, the magnesium di[tetrakis(Faryl)borate] and the triarylmethyl salt, protic ammonium salt, or onium salt are mixed together at room temperature. Mixing at room temperature is preferred because the yield of triarylmethyl, protic ammonium, or onium tetrakis(Faryl)borate is often much higher than when the mixture is heated. Some heat may be produced during the course of the reaction, raising the temperature of the mixture. The mixture may be heated, provided that the temperature does not exceed the thermal decomposition temperature of the product of the reaction. Heating during contacting of magnesium di[tetrakis(Faryl)borate] and the triarylmethyl, protic ammonium, or onium salt is preferred when a faster reaction rate is desired. Agitation of the reaction mixture is usually necessary for the reaction to proceed.
The contact time for magnesium di[tetrakis(Faryl)borate] and the protic ammonium salt or onium salt is preferably from about fifteen minutes to about eight hours; more preferred is a time in the range of from about forty-five minutes to about six hours. For mixing the magnesium di[tetrakis(Faryl)borate] and the triarylmethyl salt, the contact time at room temperature is preferably in the range of from about two hours to about thirty hours, and more preferably is in the range of from about ten hours to about twenty-four hours. A contact time for magnesium di[tetrakis(Faryl)borate] and the triarylmethyl salt when heating in the range of from about thirty minutes to about twenty hours is preferred; a more preferable range is from about one hour to about fifteen hours; highly preferred is a contact time in the range of from about two hours to about twelve hours.
From the magnesium di[tetrakis(Faryl)borate], a large variety of metal salts of the tetrakis(Faryl)borate anion may be produced from metal salts. The metal cation of the metal salt may be an alkali metal cation, an alkaline earth cation other than magnesium, or a transition metal cation. Examples of transition metal cations include silver, copper, gold, zinc, iron, palladium, nickel, and cobalt. Monovalent cations, such as alkali metal cations, silver(I), and copper(I), are preferred. Alkali metal cations are especially preferred because these salts can easily be dried, a useful feature when subsequent reactions and uses of the metal tetrakis(Faryl)borate require a dry salt. The most preferred alkali metal cations are sodium and potassium.
Suitable anions for the metal salts are almost limitless. Examples of such anions include, but are not limited to, bicarbonate, carbonate, nitrite, nitrate, phosphate, sulfite, sulfate, carboxylic acid anions (e.g., acetate, citrate, formate, oxalate, propionate, tartrate, etc.), fluoride, chloride, bromide, iodide, tetrafluoroborate, and hexafluorophosphate. Preferred anions are sulfate, bicarbonate, and carbonate; carbonate is particularly preferred. The most preferred metal salts are thus sodium carbonate and potassium carbonate. The metal salt may be combined with the magnesium di[tetrakis(Faryl)borate] in solid form or as a solution; a solution of the metal salt, particularly an aqueous solution, is preferred.
The amount of metal salt needed for reaction with the magnesium di[tetrakis(Faryl)borate] can vary with the oxidation state of the metal cation. The use of less than about one mole of positive charge per about one mole of tetrakis(Faryl)borate anion may result in incomplete exchange of the magnesium for the desired metal cation. Complete exchange is generally preferred, so at least about one mole of positive charge per about one mole of tetrakis(Faryl)borate is preferable. More preferred is the use of slightly more than about one mole of positive charge per about one mole of tetrakis(Faryl)borate anion. Thus, it is preferable to use at least about two moles of positive charge per mole of magnesium di[tetrakis(Faryl)borate]. For example, the use of at least about one mole of potassium carbonate per mole of magnesium di[tetrakis(Faryl)borate] is preferred, while at least about two moles of silver nitrate per mole of magnesium di[tetrakis(Faryl)borate] are preferable.
For syntheses of protic ammonium, onium, and triarylmethyl salts of tetrakis(Faryl)borate from metal tetrakis(Faryl)borate salts, the reaction considerations and conditions are much the same as described above for the reactions of magnesium di[tetrakis(Faryl)borate] to form protic ammonium, onium, and triarylmethyl salts.
Tetrakis(Faryl)borate salts, including protic ammonium salts in which the protic ammonium cation is without aryl groups, onium salts, and triarylmethyl salts can form liquid clathrates in combination with at least one liquid aromatic hydrocarbon. Suitable liquid aromatic hydrocarbons include, for example, benzene, toluene, xylenes, mesitylene, cumene, cymene, and indene. Toluene is the most preferred liquid aromatic hydrocarbon. A weight ratio of tetrakis(Faryl)borate salt to aromatic hydrocarbon in the range of from about 1:1.0 to about 1:3.0 is usually effective to form a stable clathrate, although it is recognized that this ratio may vary somewhat with the specific cation, tetrakis(Faryl)borate anion, aromatic hydrocarbon and temperature chosen. Excess aromatic hydrocarbon does not adversely affect the formation of the liquid clathrate, and a quantity in excess of the amount that is necessary to form the liquid clathrate is preferably used. The addition of heat is sometimes necessary to induce clathrate formation; in such cases, it is preferred to heat to a temperature below the boiling point of the chosen liquid aromatic hydrocarbon(s). Liquid clathrates that form at ambient temperatures (15 to 30xc2x0 C.) are highly preferred. The pressure during clathrate formation is typically atmospheric. These clathrates are generally stable when heated, up to a deformation temperature, such temperature varying with the particular cation, anion, and solvent chosen.
The liquid clathrate is generally formed by mixing the liquid aromatic hydrocarbon with the tetrakis(Faryl)borate salt while agitating, until a readily recoverable liquid clathrate layer, immiscible with the liquid aromatic hydrocarbon, is formed. A two-layer mixture is usually formed, and the liquid clathrate is normally the lower layer. The layers are easily separable, for example by decantation. Once separated, the addition of excess nonsolvent, such as a nonaromatic hydrocarbon, or removal of the aromatic hydrocarbon comprising the liquid clathrate from the liquid clathrate layer by methods such as vacuum distillation, usually results in the isolation of the tetrakis(Faryl)borate salt as a solid. Because the liquid clathrate layer excludes other species, it is possible to obtain very pure tetrakis(Faryl)borate salts using liquid clathrate formation as a purification method.